1. Field of the Invention
The present invention relates to an outlet nozzle for use within bowl centrifuges and, more particularly, to an outlet nozzle including an improved insert for facilitating streamlined fluid flow therethrough.
2. Description of the Related Art
Bowl centrifuges of a nozzle type typically include a rotor defining a separating chamber containing separating discs for effecting a two-fraction separation of feed slurry. The feed slurry is separated into a heavy discharge slurry, or underflow fraction, which is delivered outside the rotor by a plurality of nozzles supported within the outer wall of the rotor. A light fraction or separated liquid is removed from the rotor by overflow from the top end of the machine.
To effect proper separation of the feed slurry, it is necessary to rotate the rotor within a conventional bowl centrifuge at a high rotational speed. The high rotational speed of the rotor creates sufficient centrifugal force to separate the heavy discharge slurry outwardly to the nozzles supported within the outer wall of the rotor.
One arrangement illustrating centrifuge nozzles secured within a rotor wall is disclosed in U.S. Pat. No. 2,695,748 to Millard, the disclosure of which is incorporated herein by reference. A plurality of nozzles are mounted at regularly spaced intervals about the periphery of the rotor wall. More particularly, the rotor wall is provided with a plurality of cylindrical bores for receiving the nozzles wherein the axis of each bore is radially disposed with respect to the axis of the rotor. A lug is formed integral with the body of the nozzle for detachably securing each nozzle within the rotor wall.
The fluid pressure entering the nozzle is often in the order of one thousand pounds per square inch (psi). Consequently, this results in very high velocities in the discharge orifice of the nozzle. Such high velocities result in the requirement of a high wear resistant material for the nozzle.
Conventional nozzles comprise a holder including an axial inlet channel and an outlet channel angularly disposed relative to the inlet channel. An insert of material harder than that of the nozzle holder is typically secured within the outlet channel wherein the flow of fluid is diverted from the inlet channel to the outlet channel and out through the orifice defined by the insert. The inserts of prior art nozzles have been designed to insure that the inner surface facing the inlet channel forces the fluid flowing through the inlet channel to change direction before it can arrive at the orifice. Damage, particularly due to cavitation and erosion from impact by the fluid against the inner surfaces of the channels, frequently occurs to the nozzle holder. Traditionally, such damage may lead not only to rapid failure of the nozzle, but also to damage of the centrifuge rotor itself.
In order to reduce the wear rate of the holder, U.S. Pat. No. 5,033,680 proposes providing an outlet nozzle including a nozzle holder and means forming an orifice comprising an entry cone with a semi-circular recess on the same axis of symmetry of an intake channel, having the same radius as the intake channel, and immediately adjacent thereto.
While the outlet nozzle disclosed in U.S. Pat. No. 5,033,680 significantly reduces wear on the nozzle holder, it does not provide for an efficient flow of fluid from the intake channel to the orifice. As such, there is a need for a centrifuge nozzle having an improved insert for reducing wear to the nozzle holder and for providing a streamlined fluid flow condition from the inlet channel to the insert orifice.
The present invention provides an outlet nozzle for use within a centrifuge rotor, the outlet nozzle comprising a holder including an axial inlet channel having an inner surface and defining an inlet axis, and an outlet channel having an inner surface, defining an outlet axis, and in fluid communication with the inlet channel along an intersection. The outlet axis is disposed angularly in a non-parallel relation to the inlet axis.
An insert including a proximal end and an opposing distal end is supported by a holder. The insert is composed of a first material and the holder is composed of the second material, wherein the first material is harder than the second material. The distal end is received within the outlet channel and the proximal end extends within the inlet channel. The insert further includes an inner surface and an orifice at the distal end. The inner surface includes an orifice portion adjacent the distal end and a directing portion adjacent the proximal end. The directing portion shields at least a portion of the inner surface of the outlet channel for preventing impact therewith and for diverting fluid flow from the inlet channel of the holder and into the orifice portion of the insert.
The insert further includes an inlet edge at the proximal end which is defined by the intersection of the outlet channel and the inlet channel. More particularly, the intersection is defined as the geometric location where fluid is redirected from the inlet channel to the outlet channel. The outlet axis crosses the inlet axis at an intersection point, wherein the inlet edge intersects a directing line extending through the intersection point perpendicular to both the outlet axis and the inlet axis. The inner surface of the inlet channel includes opposing front and rear portions, wherein the inlet edge includes a first portion extending from the front portion of the inner surface to the directing line and a second portion extending from the rear portion of the inner surface to the directing line.
Objects and advantages of the invention will be apparent from the following description, the accompanying drawings and the appended claims.